The relationship between species richness, diversity and grazing frequency along an altitudinal gradient (1900-3400 m) of an Andean ecosystem indicates that there is an intense human pressure on vegetation use. To identify the vascular flora and its conservation, 20 sites were sampled in two visits during 2006. We identified 79 taxa, including 62.03% native species, 22.78% adventitious and 8.86% endemic (the remaining 6.33% was identified only at the genus level). Some genera were underrepresented. We also observed latitudinal limits (Alstremeria andina), monotypic genera (Geoffroea, Kurzamra, Phragmites, Tessaria and Salix) and monogeneric families (Buddlejaceae, Ephedraceae, Equisetaceae, Malesherbiaceae, Salicaceae and Oxalidaceae). Moreover, we found differences in the species distribution patterns during periods of grazing use and identified statistically significant differences in the species richness (p < 0.001), diversity (p = 0.010) and grazing frequency ( p = 0.047).